Hitherto, glass antennas for receiving AM radio broadcast waves and FM radio broadcast waves are often formed on a rear window glass of an automobile, since it requires a relatively large area for obtaining a good reception gain. Furthermore, the rear window glass of the automobile is often formed on its central region with defogging heater strips for ensuring rear visibility at the driving in rain. Accordingly, in case that the glass antenna is formed on the rear window glass, it has been forced to be formed on a space above or below the defogging heater strips.
Furthermore, in most cases, one antenna provided on the space above the defogging heater strips has been received radio waves of AM radio broadcast waves and radio waves of FM radio broadcast waves. This antenna of the AM radio-band/FM radio-band has been a grounded antenna pattern having one common feed point.
Furthermore, in case of receiving the radio waves of the AM radio broadcast waves and the radio waves of the FM radio broadcast waves by one glass antenna, in many cases, an antenna amplifier has been provided generally between an antenna feed point and a tuner so as to amplify an electromotive force insufficient to be input to the tuner, and it has been input to the tuner.
Alternatively, an impedance matching circuit has been formed in order to minimize the reduction loss of the reception gain by a feeder line between the antenna feed point and the tuner to maintain the electromotive force to become sufficient to be input to the tuner, thereby inputting it to the tuner.
In the case of sharing antennas of the AM broadcast waves and the FM broadcast waves, in many cases, with respect to the amplifier, an AM broadcast wave amplifier and an FM broadcast wave amplifier are separately provided, thereby amplifying the received power and then inputting it to the tuner. Alternatively, also with respect to the impedance matching circuit, in many cases, the reduction due to the loss of the reception sensitivity is suppressed by an AM broadcast wave impedance matching circuit and an FM broadcast wave impedance matching circuit in the route that the radio waves received by the antenna are transmitted to the tuner.
As one in which a glass antenna is formed on an upper space of a vehicular rear window glass and an amplification is conducted by an amplifier, for example, there is described in a microfilm of Japanese Utility Model Application No. 63-89982 (Japanese Utility Model Laid-open Publication No. 2-13311) an amplifier attachment structure of a vehicular glass antenna, which has a glass antenna in which an antenna conductor is formed at a predetermined position of a vehicular window glass sheet and an amplifier for amplifying the reception sensitivity of the glass antenna, and in which the amplifier is directly connected to a feed terminal portion of the glass antenna by means such as soldering, brazing or a conductive adhesive bonding, thereby reducing the gain loss due to the capacity loss at a feed line portion between the glass antenna and the amplifier (A Patent Document 1).
In a glass antenna for a vehicle in Japanese Patent Application Publication No. 11-205023, there are provided a first coil, a second coil, a first antenna conductor provided in a window glass sheet of a vehicle, and a second antenna conductor provided in the window glass sheet of the vehicle. This glass antenna generates first resonance including, as resonance elements, impedance of the first antenna conductor and inductance of the first coil, and generates second resonance including, as resonance elements, impedance of the second antenna conductor and inductance of the second coil. The second antenna conductor has a length and a shape of the conductor for a first received frequency band. The first antenna conductor has a length and a shape of the conductor for a second received frequency band higher in the frequency than the first receiving frequency band. A resonance frequency of the first resonance and a resonance frequency of the second resonance are, respectively, frequencies to improve the sensitivity of the first received frequency band. The first antenna conductor and the second antenna conductor are electrically connected with each other (A Patent Document 2).
Patent Document 1: a microfilm of Japanese Utility Model Application No. 63-89982 (Japanese Utility Model Laid-open Publication No. 2-13311)
Patent Document 2: Japanese Patent Application Publication No. 11-205023